The work presented in the thesis is concerned with the application of the variational analysis to the problem of developed steady flow in a helical screw extruder. By using the helical system of coordinates the problem is reduced to a two-dimensional one and the channel is treated in its true helical geometry thus eliminating the unwrapped-channel approximation, and making the solutions applicable to both shallow and highly curved channels. The constrained extremum approach is adopted, in which the continuity equation is incorporated into the functional, which is then applicable to non-isothermal and purely viscous flows. Minimization is carried out using the finite element method. A computer programme is developed to perform the velocity solution which takes into consideration the computer speed and storage requirements. Investigations are then carried out to test the validity of the present approach. Results for the Newtonian isothermal flow in shallow and highly curved channels are obtained, and successfully compared with known solutions and experimental findings, in terms of both the flow characteristics and velocity profiles. Solutions are also given for non-Newtonian isothermal flows in shallow and deep channels, using a power-law model, and compared with experimental and other numerical results. Leakage flow is studied and results are compared with the analytical models developed for shallow channels. The non-isothermal flow problem, including thermal convection, is formulated and the case of thermal conduction and heat dissipation is solved. The results obtained have established the validity of the present approach which can be extended to cover the general non-Newtonian, non-isothermal flow problem.

Finite amplitude wave motion in an inviscid, subsonic, perfect gas medium is analysed by explicit finite-difference methods. A series of one-dimensional problems are used to examine the accuracy of the algorithms when applied to unsteady flow regimes. Computations are carried out in two space dimensions using a two-step, Lax-Wendroff algorithm. The computed flow field has similarities with that which occurs in the vicinity of an isolated rotor in an axial-flow compressor stage. The rotor effect is simulated by prescribing either a velocity or a pressure disturbance along a single row of grid points normal to the stream direction and results in 'forced' outflow boundary. Particular emphasis is placed on devising a simple non-reflecting, far-field inflow boundary treatment. This is achieved by using a streamwise expanding grid to place the inflow boundary at a large distance from outflow in a position where wave amplitudes are negligible. The side boundaries are spatially periodic. The computed solutions are compared with analytical, small-perturbation solutions; higher-order effects arising from non-linearities are revealed by Fourier analysis. Solutions which closely approached a periodic state were obtained. The two-step Lax-Wendroff method combined with the expanding grid is shown to be accurate and stable. The use of the computational procedures for the accurate resolution of unsteady flow through a turbo-machinery cascade is discussed.

In the recovery of essential oils from vapour and nitrogen streams by cooling, an aerosol is formed. The work described is a study of aerosol formation and the subsequent aerosol collection process for the oil geraniol (C10H130). Vapour at concentration up to 0.03 g/g N2 was cooled and up to 35% of it changed into aerosol having a weight-moment mean diameter, Dwm, of up to 5.1 pm. Results showed that particle size increased with decreasing vapour cooling rate; and that particle size and mass concentration increased with initial vapour concentration. Studies of filter collection efficiency were conducted with a geraniol aerosol of Dwm = 1.0 pm. Its particle number concentration was high, at about 5x10 .//cc N2. Filters used were: (1) glass sintered discs of 50 pm and 110 pm maximum pore size; (2) fibrous filters of 0.004-0.13 packing density and 0.07-12.2 cm thickness made of "Bekinox" stainless steel fibres of 4-22 pm diameter. Filtering area was about 3.1 cm2 and superficial velocity up to 110 cm/s. Filter resistance, liquid saturation which resulted from collecting aerosols, and collection efficiency were determined. For disc filters, resistance and efficiency increased with decreasing pore size. Wetted filter resistance was approximately correlated with disc porosity and simplified capillary number N'a (Qu/At). For fibrous filers in stationary filtration condition, resistance data fitted closer with Davies' empirical model, and efficiency data were close to theoretical values based on the Rappel-Kuwabara flow field. In the non-stationary filtration condition (wet) and at packing densities a > 0.02, liquid saturation correlated with capillary number and a proposed dimensionless group (al/df), and filter resistance correlated approximately with N4ap and (al/df). The efficiency of filters of low packing density (a<0.02) was apparently not affected by liquid saturation, but the efficiency of high packing density filters was increased to varying degrees. For a>0.04, collection efficiency data fitted closely with a proposed model which is based on existing filtration theories with modified parameters including liquid saturation, fibre diameter and superficial velocity.

No description available.

This work presents the results of an experimental study of liquid distribution with counter-current gas flow and without gas flow, carried out in a 0.3m diameter and 1.5m long perspex column packed randomly with 1" plastic Pall rings, 1" plastic Intalox saddles, No.25 Intalox Metal Tower Packing(IMTP) and No.1 metal Nutter rings, in separate experimental sets. The measurements were carried out using concentric annular collectors, in order to measure the distribution of liquid and to distribute the gas uniformly across the bottom of the column. The column was operated with gas flowrates varying over the range of 0 to 1 kg/m<SUP>2</SUP>.sec, and liquid flowrates varying over the range of 40 to 80 1/min. Packing height was increased by adding successive layers of packing, while the ratio of the flow supplied to the bulk and wall regions was varied throughout the experiments. The experimental results were analyzed and compared to a theoretical model developed by Gunn(1978) and extended in 1991. Two regions of packing of different permeabilities may be distinguished, the bulk region and an annular region of packing adjacent to the wall and of higher permeability. The wall region was confined to the order of one particle diameter while the remaining cross-section of the column was accounted as the bulk region. The separation of volumetric mass transfer coefficients in packed columns into mass transfer coefficients and specific surface area, has been attempted using the available data on mass transfer presented by various investigators. One aim of this work is to provide a generalized correlation for mass transfer coefficients and interfacial area that characterized the mass transfer performance of various packings that may be used for designing or scaling up columns or reactors.

An electron microscopic study of Na-attapulgite particles showed their lath-like habit with aspect ratios of approximately 100:3:1 (length:width:thickness). The average length of the particles is 0.951 μm. The nature and density of titratable surface charge was studied using an automatic potentiometric and titration apparatus. The results revealed that both positive and negative charges develop at the edges of the particles. The point of zero net proton charge (PZNPC) of the edges is at pH 6~7 depending on the electrolyte (NaCl) concentration (<I>c</I>). Electrophoretic mobility determined (using a Malvern Zeta Sizer II) over a range of pH and electrolyte concentrations showed a significant influence of the edge titratable charges on the electrokinetic properties. Particle size analysis (in suspension) using the technique of photon correlation spectroscopy (PCS) suggested that measurements of mobility reflect the electrokinetics motion of single laths at pH<6 and c<10<SUP>-3</SUP> NaCl. However small aggregates form the electrokinetic units at pH<6 and/or high electrolyte concentrations. Conversion of mobility to zeta potentials proved difficult due to the lack of a suitable theory for the electrophoresis of lath-like and non-uniformly charged particles. An approximate method (Williams & Williams, 1978) was applied for resolving zeta potentials into separate face and edge components. The linear viscoelastic behaviour of concentrated Na-attapulgite suspensions was investigated using the techniques of shear wave propagation and forced non-resonant dynamic oscillation.

No description available.

No description available.

Osmotic pressure and diffusion coefficients were studied experimentally and theoretically in order to facilitate fully quantitative descriptions of ultrafiltration processes. These parameters may be incorporated in the solution of the equations for hydrodynamics and mass transfer in the filtration module. Theoretical descriptions are presented to allow calculation of osmotic pressure, taking account of the electrostatic repulsive interactions, London Van Der Waals forces, configurational entropy and additional interactions of unknown source. Approaches of constant zeta potential and charge regulation conditions were investigated for BSA, lactoferrin and silica colloidal dispersions. An experimental technique for measuring osmotic pressure was established and verified by comparison of the measured osmotic pressure with known data using BSA protein dispersions. The measured osmotic pressures of BSA solutions also agreed well with the theoretical predictions. Osmotic pressures of the commercially important protein lactoferrin solutions were also measured. Using the experimental results further refinement of the charge regulation model was made by modifying the expression of the extra attractive force, which is probably caused by interaction between sugar molecules on the protein surfaces. The refined model gives greatly improved prediction of osmotic pressure as well as ultra-filtration rate over a wide range of solution conditions. Osmotic pressures of silica dispersions were also measured and a charge regulation model was developed for the silica colloidal system. This model gives a good description of the experimental results over the conditions studied. The gradient diffusion coefficients of BSA solutions were measured by the modified Taylor's capillary method and compared with light scattering data. An analysis of electrokinetic effects in membrane pores containing electrolytes has also been carried out. The analysis uses a numerical solution of the non-linear Poisson-Boltzmaan equation and allows for the mobilities of anions and cations to be individually specified. It is shown that it is very important to use such an approach to calculate zeta-potentials from the basic electrokinetic data.

This thesis is concerned with the numerical simulation of Newtonian and viscoelastic free-surface flows. This work is novel in advance of hybrid finite volume and free-surface techniques, and in the study of particular industrial flows. The presence of free-surfaces in a number of complex industrial flows, gives rise to instabilities during processing. Consequently, these instabilities impose certain limitations on processing windows and final product quantity. Accordingly, an important aspect of the current work is to investigate these instabilities, with a view to suggesting possible remedies for suppression. A transient semi-implicit Taylor-Galerkin/pressure-correction time-stepping framework is employed, accommodating both finite element (FE) and finite volume (FV) schemes. FE discretisation is used for the momentum-continuity equations, whilst the constitutive equations are resolved through finite volume cell-vertex approximation. To quantify the accuracy, stability and consistency of the proposed FV method, we have chosen a model sink-flow problem, that has an analytical solution. Our interest is to explore the consequences of utilising conventional cell-vertex methodology for an Oldroyd-B model and to demonstrate deficiencies in the presence of complex source terms. In this manner, a consistent approach is derived. The first complex problem addressed is that of industrial reverse-roller coating for Newtonian viscous flows. The evolving position of the free-surface, whose position is unknown a <I>priori, </I>is computed using kinematic boundary adjustment with mesh-stretching algorithms. The problem is analysed first to steady-state, prior to transient considerations. We have found pressure maxima to arise in the nip region, that subsequently produce elevated levels of lift on the foil. In addition, we have investigated the influence of these elevated forces (lift) on the foil, by adjusting nip-width in time. Variation in nip-gap width introduces temporal foil-vibration. This is found to have a significant impact upon pressure and lift on the foil. Such temporal changes in nip-width, also generated free-surface instabilities that act upon the coating layer (film-thickness). A second problem studied is that associated with filament-stretching flows. The long-time, large extensional deformations and break-up of Newtonian fluids is analysed, based on an axisymmetric, time-dependent half-length model. The simulation is performed between two plates, which depart at an exponentially increasing rate. Due to the presence of rigid-end-plates and imposed pinning boundary conditions, the radius of the filament varies along its length. Ultimately, this leads to filament break-up. Various remeshing schemes have been introduced. A cost-effective approach is proposed, that suppresses premature filament breakup and maintains accuracy and stability within the computer predictions up to large Hencky-strain levels. Finally, attention is turned to filament-stretching for viscoelastic fluids. Here, we have recourse to the hybrid FE/FV approach and a coupled/decoupled algorithm is outlined. Various aspects of the problem are addressed and results are compared against those for Newtonian fluids, considering a full-length model. With regard to upwinding discretisation, we have contrasted performance of both LDB and LAX-Wendroff schemes. An optimum choice has emerged that captures stress field accurately in the vicinity of the free-surface.